Large out-of-plane spin polarization in a spin-splitting one-dimensional metallic surface state on Si(557)-Au

We report evidence of a spin-split one-dimensional metallic surface state for the system of Si(557)-Au obtained by means of spin- and angle-resolved photoelectron spectroscopy. Strikingly, considerably large out-of-plane spin polarization which is locked to one specific direction has been observed which is in good agreement with the one-dimensional Rashba spin-splitting surface states caused by the highly anisotropic wave function of the gold chains predicted by first-principles calculation.